As Americans take more imaging tests, how much radiation is too much? And at what cost?

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Debbie Liebross describes herself as a bit of “a cancer phobic.” And she has reason to worry. Her mother died of lung cancer at age 69, and Liebross was once a social smoker, although she kicked the habit early.

To keep anxiety at bay, the 55-year-old resident of Fort Lauderdale, Fla., has gotten a chest x-ray every few years for at least a decade to check out her lungs. Last year, when her family doctor suggested a baseline CT (computed tomography) scan of her heart to identify any developing problems, she decided to get her lungs scanned as well.

Thousands of Americans like Liebross undergo imaging tests each day without hesitation. Costly medical imaging has become increasingly—and sometimes unnecessarily—commonplace. As a result, Americans today are exposed to seven times more radiation, via medical tests, than they were in the early 1980s, according to a report released this spring by the National Council on Radiation Protection and Measurements.

“People can be exposed to a large amount of radiation,” says Timothy Bullard, M.D., an emergency room physician in Orlando, Fla., who has studied radiation exposure in patients. “They don’t realize it. Nor do the physicians. We don’t have any good way of tracking it right now.”

But when radiation exposure is involved, how much is too much? And how does one weigh relative risks and benefits, particularly in light of proliferating imaging options?

A study published Aug. 27 in the New England Journal of Medicine, looking at nearly 1 million patients ages 18 to 64 over a three-year period, found that radiation exposure from medical imaging tests can leave the body with higher cumulative doses than previously thought. Nearly seven out of every 10 adults—69 percent—had gotten at least one imaging scan during that period. The oldest in the group, ages 55 to 64, were most likely to have higher doses. The study estimates that at least 4 million Americans are exposed to high doses of radiation each year from medical imaging tests.

The study’s findings, and those of previous studies, point to “tens of thousands of cancers” related to medical imaging, says Rita Redberg, M.D., a medical imaging researcher at the University of California, San Francisco, who is not connected to the study.

Individual risk depends on the number and the types of scans, as well as the age at which the exposure begins, Redberg says. Malignancies can take a number of years to develop.

Patients who have had a number of CT scans—tests that produce cross-sectional images of the body—are most at risk.

“I would be more concerned if you’ve had a number of CT scans—definitely,” says Redberg. “The idea is you want to limit your lifetime radiation exposure.”

Cancer risks, imaging costs

The average radiation dose per American from all sources, including background radiation, rose from 3.6 to 6.2 mSv (millisieverts) from the early 1980s to 2006—primarily due to imaging tests, according to the council’s findings.

Another report, published last year by the Government Accountability Office, focused on the price tag. From 2000 through 2006, Medicare spending for imaging slightly more than doubled, reaching $14 billion. When experts discuss reducing wasteful spending in Medicare, unnecessary imaging is often toward the top of the list. The spending for some of these tests increased significantly faster than x-rays and ultrasound.